I have knitted using all 3: NP, Harmony, and Zephyr.
Zephyr needle tips "knit like" Harmony needles. If someone needs a needle with a little bit of drag on the surface, Zephyrs would be suitable.
Yeah, not a pretty as Harmony...but they wouldn't fall apart either. The crystal clear acrylic has its own beauty!
BTW: My Harmony's have been very dependable. No issues whatsoever. It should be disclosed that I spend 95% of my knitting time using NP, either KP or Addi.